Studies on the cell cycle-dependent regulation of plant DHFR/TS genes

Arabidopsis thalianacontains threedhfr/ts(dihydrofolate reductase/thymidylate synthase) genes showing divergent patterns of expression. Analyses of promoter activity in transgenic plants have revealed that only theAtDRTS2promoter can drive a strong proliferation-specific expression in both root and shoot apical meristems. In contrast,AtDRTS1is highly expressed in vascular tissues but not in the meristems, whereasAtDRTS3showed strong expression in the shoot meristem but not in the meristems of the roots, where its activity was confined to the columella and the central cylinder. TheAtDRTS2andAtDRTS3promoters contain E2F binding sites which, according to ChIP analyses, are recognizedin vivoby E2F factors. Functional analyses performed in transgenic plants have revealed a repressive role of these sites in the control of the expression of bothAtDRTS2andAtDRTS3. Additionalcis-acting elements have been identified in theAtDRTS2promoter and appear to up-regulate its meristematic expression. Moreover, expression of theAtDRTS2gene depends on the presence of a small region of the first intron which shows no similarity to other known plantcis-elements.